1. Field of the Invention
The present invention relates to a light emitting display device and a stem advantageously used for the preparation of the light emitting display device. Particularly, the invention relates to a light emitting display device (which is also called "display lamp" or "display") having high luminance and high distinguishability, and a stem advantageously used for the preparation of the light emitting display device.
2. Description of Prior Art
Light emitting display devices to indicate various signals, symbols and numerical values, which have been used for various displays such as an instrument panel of airplane, need to have high luminance and high distinguishability. A conventional device comprises a combination of a plural number of fine bar filaments or small lamps. Examples of such light emitting display devices using a combination of a plural number of fine bar filaments or small lamps are shown in FIG. 1 and FIG. 2.
As is shown in FIG. 1, in the light emitting display device using bar filaments, a plural number of pairs of electrically conductive posts 12 are provided on a base plate (or container) 11 and a filament 13 is strung between each pair of posts. Usually, the surface of a light emitting display device is covered with a transparent lid panel and the condition surrounding a filament is made vacuum in order to protect the filament. Although the light emitting display device using bar filaments has simple constitution and exhibits uniform luminance, there is a case that the display is not easily recognizable, since the light emitting face of the filament is very narrow.
On the other hand, as is shown in FIG. 2, in the light emitting display device using small lamps, slender small lamps 23 are provided on a base plate (or container) 21. The light emitting face of the light emitting display device of this type is almost a rectangle and is so large that the display indicated by the device is easily recognizable. However, the device of this type has a defect that luminance of each light emitting face is apt to be not uniform, since the degree of vacuum in each small lamp employed varies from each other.
In order to solve the above-mentioned problems, the present applicant invented a light emitting display device comprising a container having a plural number of chambers, wherein a filament is arranged in each chamber so that an opening of each chamber can constitute one component of light emitting face; and already applied for patent (Japanese Patent Provisional Publication No. 62(1987) 113355). As is shown in FIG. 3, FIG. 3A and FIG. 3B, the device comprises a container 33 having chambers 32 which are defined by a plural number of walls 31. A filament 34 is arranged in each chamber 32, and the container 33 is covered with a transparent lid panel 35. In order to unify the degree of vacuum in each chamber, ditch 36 is provided on the base portion 33a of the container 38 and thin pipe 38 is provided in the ditch 36. The thin pipe 38 has apertures 37 in every constant distance so that each chamber can have the aperture, whereby gas can freely flow among the chambers through the pipe. By using the exhaust pipe 39 provided in a certain chamber, the inside of the container 33 can be made vacuum and the inside of every chamber can be made uniformly vacuum. Therefore, the luminance of each light emitting face can be kept uniform.
The above-described known light emitting display device is very useful, because its light emitting face can be made to give any shape and size (volume, length, width, etc.,) and the luminance of each light emitting face can be kept uniform. However, the production cost of the display device is considerably high, because the process for the preparation of the device is complicated.
In more detail, the process for preparing the light emitting display device shown in FIG. 3 comprises; a step of burying thin pipe 38 having a plural number of apertures 37 into the ditch 36 which has been beforehand provided on the base 33a, a step of preparing a stem by fixing a frame body onto the base 33a to form the side wall of the container 33 and walls 31, a step of arranging filaments to prepare a stem member, a step of providing a transparent lid panel onto the stem member and a step of exhausting air to make the inside of the container vacuum.